Quote Originally Posted by Diapositivo View Post
"Experience" seems to suggest that the piano is going to be well exposed.
My (shaky) understanding of physics seems to suggest to me that the light reflected by the piano should indeed obey to the inverse square law, and the reading I take with the incident light meter should produce underexposure. If we had placed the lamp at twice the distance, the light we would have measured would have been 2 stops less. Now we walk 300 m away from the piano reflecting our light in all directions, we should observe a fall of light reflected from the piano with distance.
We do!
There is less light, reflected off the piano, reaching the camera than at 150 m, or 10 m.
But don't forget that the image of that piano will be proportionally smaller.
As mentioned before: both image size and light intensity follow the same geometry. So though there's less light, that light has to fill in a smaller spot on film. The intensity per area unit will be the same at 300 m as it would be at 150 m, or 10 m.
So the setting to use is the same too.